How do I remove data and log-in info from my loaner MacBook Pro?

Had to take my Macbook Pro in for repairs. They gave me a loaner to use and I signed into it with my Apple ID to get all of my 'stuff' for school. The repair is done and I can pick up my Macbook. How do I remove my data and log-in info from the loaner Macbook?

[Re-Titled by Moderator]